Shot shell external corrosion - General Ammunition Discussion

What are these calcium looking buildups? I cleaned the one on the left. And it appears there is no cartridge wall breach (no hole). They are all live “REM-UMC No.12 Best” headstamped.

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Shot shell external corrosion - General Ammunition Discussion - International Ammunition Association Web Forum

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Shot shell external corrosion - General Ammunition Discussion - International Ammunition Association Web Forum

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